Future atmospheric methane concentrations in the context of the stabilization of greenhouse gas concentrations

Abstract. Tropospheric CH 4 concentration depends, according to modeled tropospheric processes, on many factors, including emissions of CH 4 as well as NO x and CO. Illustrative analyses of the relation between emissions and CH 4 concentration give some guidance on the role of CH 4 in the stabilization of greenhouse gas concentrations. The contribution of CH 4 to radiative forcing at the time of stabilization is expected to be modest, provided CH 4 and CO emissions do not go far beyond current rates. However, in cases leading to stabilization the potential mitigation of increases in radiative forcing by methane control could be comparable to that of CO 2 control over the next century. Whether or not this potential is realized will depend partially on the cost of deep reductions of CH 4 , NO x , CO, or CO 2 emissions over the next century, which is not known

On strategies for reducing greenhouse gas emissions

Equity is of fundamental concern in the quest for international cooperation to stabilize greenhouse gas concentrations by the reduction of emissions. By modeling the carbon cycle, we estimate the global CO(2) emissions that would be required to stabilize the atmospheric concentration of CO(2) at levels ranging from 450 to 1,000 ppm. These are compared, on both an absolute and a per-capita basis, to scenarios for emissions from the developed and developing worlds generated by socio-economic models under the assumption that actions to mitigate greenhouse gas emissions are not taken. Need and equity have provided strong arguments for developing countries to request that the developed world takes the lead in controlling its emissions, while permitting the developing countries in the meantime to use primarily fossil fuels for their development. Even with major and early control of CO(2) emissions by the developed world, limiting concentration to 450 ppm implies that the developing world also would need to control its emissions within decades, given that we expect developing world emissions would otherwise double over this time. Scenarios leading to CO(2) concentrations of 550 ppm exhibit a reduction of the developed world's per-capita emission by about 50% over the next 50 years. Even for the higher stabilization levels considered, the developing world would not be able to use fossil fuels for their development in the manner that the developed world has used them

Worldwide Maize and Soybean Yield Response to Environmental and Management Factors Over the 20th and 21st Centuries

A land process model, Integrated Science Assessment Model, is extended to simulate contemporary soybean and maize crop yields accurately and changes in yields over the period 1901–2100 driven by environmental factors (atmospheric CO2 level ([CO2]) and climate), and management factors (nitrogen input and irrigation). Over the twentieth century, each factor contributes to global yield increase; increasing nitrogen fertilization rates is the strongest driver for maize, and increasing [CO2] is the strongest for soybean. Over the 21st century, crop yields are projected under two future scenarios, RCP4.5-SSP2 and RCP8.5-SSP5; the warmer temperature drives yields lower, while rising [CO2] drives yields higher. The adverse warmer temperature effect of maize and soybean is offset by other drivers, particularly the increase in [CO2], and resultant changes in the phenological events due to climate change, particularly planting dates and harvesting times, by 2090s under both scenarios. Global yield for maize increases under RCP4.5-SSP2, which experiences continued growth in [CO2] and higher nitrogen input rates. For soybean, yield increases at a similar rate. However, in RCP8.5-SSP5, maize yield declines because of greater climate warming, extreme heat stress conditions, and weaker nitrogen fertilization than RCP4.5-SSP2, particularly in tropical and subtropical regions, suggesting that application of advanced technologies, and stronger management practices, in addition to climate change mitigation, may be needed to intensify crop production over this century. The model also projects spatial variations in yields; notably, the higher temperatures in tropical and subtropical regions limit photosynthesis rates and reduce light interception, resulting in lower yields, particularly for soybean under RCP8.5-SSP5. © 2021. The Authors.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Climate and carbon budget implications of linked future changes in CO2 and non-CO2 forcing

The approximate proportional relationship between cumulative carbon emissions and instantaneous global temperature rise (the carbon budget approximation) has proven to be a useful concept to translate policy-relevant temperature objectives into CO _2 emissions pathways. However, when non-CO _2 forcing is changing along with CO _2 forcing, errors in the approximation increases. Using the GCAM model to produce an ensemble of ∼3000 scenarios, we show that linked changes in CO _2 forcing, aerosol forcing, and non-CO _2 greenhouse gas (GHG) forcing lead to an increase in total non-CO _2 forcing over the 21st century across mitigation scenarios. This increase causes the relationship between instantaneous temperature and cumulative CO _2 emissions to become more complex than the proportional approximation often assumed, particularly for low temperature objectives such as 1.5 °C. The same linked changes in emissions also contribute to a near-term increase in aerosol forcing that effectively places a limit on how low peak temperature could be constrained through GHG mitigation alone. In particular, we find that 23% of scenarios that include CCS (but only 1% of scenarios that do not include CCS) achieve a temperature objective of 1.5 °C without temperature overshoot

Global perspective

International audienc

Emissions and Atmospheric CO 2 Stabilization: Long-Term Limits and Paths

carbon cycle, CO 2 , emissions, scenario, stabilization,